1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more specifically to an improved method of manufacturing a semiconductor device with corrosion resistivity, in which isopropyl alcohol-containing gas is employed for ashing of a photoresist mask layer, whereby corrosive chlorine resulting from an etching process is effectively removed.
2. Description of the Background Art
Aluminum or aluminum-containing alloy has been generally known as a material for a metal film which forms electrodes on a silicone substrate of semiconductor devices. In the manufacturing process for such semiconductor devices, the film made of aluminum or aluminum-containing alloy is subject to dry etching by using a chlorine-containing gas. After the dry etching, chlorine remains in the film and also in a photoresist layer formed on the film in the form of a chlorine-containing reaction product. Chlorine reacts with atmospheric moisture to generate hydrogen chloride HCl which causes corrosion of the film so that characteristics and performance of semiconductor device are deteriorated.
In order to prevent such corrosion of the aluminum film after dry etching, there have been proposed the following measures for removing chlorine remaining in the aluminum film.
One measure disclosed is that, after dry etching with chlorine gas, the aluminum film exposed through openings of the photoresist layer are further subjected to plasma etching using fluorine gas (such as CF.sub.4) such that chlorine remaining in the photoresist layer and the aluminum film is replaced with the fluorine in the fluorine gas. However, some chlorine remains unreplaced with fluorine.
Another measure disclosed is that, after dry etching with chlorine gas, the photoresist layer remaining on the aluminum film is subjected to in-line ashing to be removed from the aluminum film. However, a chlorine-containing reaction product, generated by the dry etching, still tends to remain in the aluminum film.
Still another measure disclosed is that, after the in-line ashing mentioned previously, the aluminum film exposed through the photoresist layer, is provided with a carbon-containing passivation layer which is formed by decomposition reaction with plasma gas such as CHF.sub.3. However, the passivation layer does not completely protect the aluminum film from exposure to atmospheric moisture which reacts with a chlorine-containing product remaining in the aluminum film.
Further, another measure disclosed is that after the in-line ashing described above, the aluminum film exposed through the photoresist layer is subject to baking under vacuum such that chlorine in a chlorine-containing reaction product remaining in the aluminum film, is removed. However, even in this case the chlorine is not completely removed from the aluminum film.
Therefore, there has been disclosed an alternative measure in which, upon the in-line ashing described above, a mixture of oxygen gas and methyl alcohol CH.sub.3 OH is used as an ashing gas such that a chlorine-containing reaction product AlOxCly remaining in the aluminum film is decomposed by a reaction as indicated by the following equation: ##STR1##
However, this measure, suffers from the drawback that, as the boiling point of Al(OCH.sub.3).sub.3 is relatively high, i.e., about 240.degree. C., the chlorine-containing reaction product AlOxCly is not readily decomposed nor removed from the aluminum film. Therefore, it must be heated at a high temperature after the ashing, in order to obtain an aluminum film having sufficient corrosion resistivity.